1. Field of the Invention
The present invention relates to a method for compensating a regenerative braking amount when a regenerative braking of a vehicle fails and, more particularly, to such a compensating method when regenerative braking fails due to an error in controller area network (CAN) communications between an electronic brake system (EBS) and a hybrid control unit (HCU
2. Description of Related Art
In general, an electric vehicle means a vehicle that drives a motor using electric energy stored in a battery and uses the driving force of the motor as a power source wholly or partially.
At present, the electric vehicle is classified into a pure electric vehicle that applies only the electric energy of the battery as the power source and a hybrid electric vehicle that includes an internal combustion engine to apply the power generated from the engine to the battery charge and/or to the driving of the vehicle.
In the specification of the present invention, the term of the electric vehicle denotes the pure electric vehicle distinguished from the hybrid electric vehicle in a narrow sense and the electric vehicle in a broad sense includes the pure electric vehicle and the hybrid electric vehicle and, further, it is used to denote any vehicle in which at least one battery is established and the electric energy stored in the battery is used as a driving force of the vehicle.
That is, in a vehicle driven by a main or auxiliary driving power of the electric motor, the general electric vehicle and the hybrid electric vehicle are called the electric vehicle, and the driving motor plays a role of driving the vehicle and, at the same time, performs the regenerative braking in reducing the vehicle driving speed as well, thus collecting the kinetic energy and storing the same.
In general, the electric vehicle in braking applies a portion of braking force to the generation of electric power and uses the generated electric energy in charging the battery. Here, a portion of the kinetic energy is used as energy required for driving an electric generator, thus realizing the reduction of the kinetic energy (i.e., the reduction of the driving speed) and the generation of electric energy at that same time.
The braking method as described above is called the regenerative braking.
The generation of the electric energy in the regenerative braking mode is achieved by a separate electric generator or by driving the motor reversely.
By the regenerative braking control in braking the electric vehicle, the available driving distance of the electric vehicle is increased and, in case of the hybrid electric vehicle, the fuel efficiency is improved and the generation of noxious exhaust gas is reduced as well.
Meanwhile, a hydraulic brake system that causes a braking force by the hydraulic pressure may be equipped in the electric vehicle; however, such a hydraulic brake system may not attain a sufficient braking force only with the regenerative braking force, since a desirable vehicle dynamics control cannot be obtained only with the braking force of the driving wheels as the regenerative braking force is generated in the driving wheels connected to the motor.
In a normal state, the braking force (the operation of the brake pedal) that the driver wants is made by the sum total of the hydraulic braking force and the regenerative braking force. Accordingly, if a desired braking force is not obtained due to the limitations in the motor, battery, etc., the hydraulic braking force that generates thermal energy by the frictional force of a disc and a pad is applied as much as its difference, and the regenerative braking force operates the electric generator when reducing the speed of the driving motor dedicated to the drive to generate the necessary braking force and, at the same time, the electric power generated at this time is stored in the battery.
In general, the motor of the electric vehicle acts as an electric generator to produce the necessary braking forces of the whole vehicle. If the braking force control is not achieved by the motor connected with the general brake such as the existing hydraulic brake, etc., the driver cannot obtain a desired braking feel as he or she additionally feels a speed reduction as much as the braking force by the regenerative braking, and further the driver may always feel that the vehicle is suddenly stopped during the electric power generation by the motor.
To prevent such a problem, it is necessary to provide a braking force cooperative control between a regenerative braking torque controller taking charge of the regenerative braking of the motor a the hydraulic braking torque controller of the brake system.
However, if there occurs an error in data communications between the regenerative braking torque controller and the hydraulic braking torque controller that performs the frictional braking in the normal state and thereby the cooperative control fails (error, shortage, etc.), the hydraulic braking torque is sharply increased and, at the same time, the regenerative braking torque is suddenly lowered to a zero level, thus decreasing the braking force or the braking feel remarkably.
Paying regard to the above circumstances, a braking torque control system having a regenerative braking torque generator and a frictional braking torque generator has been disclosed in U.S. Pat. No. 6,086,166. Such a control system controls the total braking torque when there is a failure in exchanging data between the regenerative braking torque generator and the hydraulic braking torque generator; however, it controls to reduce the target regenerative braking torque.
That is, in U.S. Pat. No. 6,086,166, there has been disclosed a method of decreasing the regenerative braking torque generated in a motor gradually to an end time of braking and increasing the hydraulic braking torque gradually to the end time of braking when there occurs a failure (error, shortage, etc.) in the data CAN communications between the regenerative braking torque generator and the hydraulic braking torque generator, thus preventing the braking force from being reduced and the braking feel from being changed.
However, the above-described method and system have drawbacks in that the energy recovery rate by the electric power generation of the motor is lowered as the regenerative braking torque is decreased when the CAN communication fails and, in effect, it is impossible to perform a hydraulic control for accurately matching the increment or the decrement of the regenerative braking torque and the hydraulic braking torque with each other, thus causing changes in the braking feel due to fluctuations in the regenerative braking torque and the hydraulic braking torque.
Meanwhile, as another conventional technique related to the regenerative braking, Japanese Patent Publication No. 1999-004503 has disclosed a structure in which a regenerative braking torque is reduced when an abnormality occurs in information interchanges between a regenerative braking device and a hydraulic braking device.
Moreover, Korean Patent Publication No. 2002-0091799 has disclosed a braking force control apparatus in which a target regenerative braking force is gradually reduced and a target frictional braking force is gradually increased, if it is quite likely that an anti-skid control will be started afterwards, whereas, the target regenerative braking forces are set as 0, if the anti-skid control is started.
Furthermore, Japanese Patent Publication No. 1995-149209 has disclosed a regenerative braking system in which, when an abnormality in a regenerative braking system takes place, a clutch connecting the regenerative braking system with a driving system is controlled to issue an alarm of the abnormality of the regenerative braking system.
In addition, Japanese Patent Publication No. 2000-156901 has disclosed a structure of controlling a brake and a motor by periodically calculating an available regenerative braking amount in accordance with a remaining capacity of a battery and a driving state of the motor so as to set a regenerative torque of the motor from a brake torque and the available regenerative braking amount during the brake operation.
However, the above-described conventional arts have drawbacks in that the regenerative braking amount is always reduced and thereby the charging amount of the battery is restricted when the CAN communication fails or there occurs a failure in that the regenerative control is not available.